Topography Of Short Hepatic Veins And Interface Veins For Safe Tunneling During Hanging Maneuver Of Liver

for Social Sciences version 20 (SPSS-20). Results: The average length of retro hepatic IVC was 49.5±10.5 mm and the diameter of 25.6±4.4 mm. The inferior right hepatic vein was present in 60% of cases while the Caudate vein was present in 85% of cases. Fossa venacava had an average distance of 12.3±3.46 mm and the Vein gap was 18.9±7.1 mm. Conclusion: While tunneling between IVC and the liver, Fossa venacava could be as small as 4.6 mm. The shortest distance of the Vein gap could be as small as 5.8 mm. The intermediate course of forceps insertion is safer than the right or left course.


Introduction
Conventionally, liver resection is done by removing the liver and detaching it from Inferior Venacava (IVC) by ligating each interface vessels that directly drain into IVC. 1 This conventional approach leads to rotation of hepatoduodenal ligament causing ischemia of remnant liver, dissemination of tumor, and avulsion of hepatic veins. During large tumors approach liver resection is utilized and hanging maneuver liver resection eases the procedure of anterior approach. 2,3 For hanging maneuver in liver resection a retro-hepatic tunnel is created at the interface between liver and IVC. Through this tunnel, an elastic tape is passed which serves as a pulley in retracting liver downward. While creating this tunnel, there are multiple vessels that arise in the interface of liver and IVC. So, there is always a risk of Injuring these vessels while tunneling. 4 A detailed anatomical knowledge of retro-hepatic IVC and short hepatic veins are necessary for surgeons before performing hanging maneuver.

Right hepatic vein (RHV), Middle hepatic vein (MHV) and
Left hepatic vein (LHV) are the three major hepatic veins that drain into IVC. Most of the time middle hepatic vein forms a common trunk with LHV. 5 On the right side, there may be a Middle right hepatic vein (MRHV) and Inferior right hepatic vein (IRHV) and on the left side, there is a Caudate vein (CV) and multiple tiny Short hepatic veins (SHV). MRHV, IRHV, CV, and SHV arise at the interface of the liver and IVC so we collectively call them Interface veins. These interface veins will appear along the course of tunneling and there is always a risk of bleeding when inserting the forceps. 5 There is a space between the middle and right hepatic vein which provides a potential space for inserting forceps. This space is called Fossa venacava. 6 Along the course of tunneling the interface vessels appear. The major Interface vessels are Caudate vein on left side and inferior right hepatic vein on right side. Forceps should be inserted between IRHV and Caudate vein. A horizontal distance between IRHV and Caudate vein provides a safe gap which is known as a Vein gap or tunneling gap or free zone. [6][7][8] Hepatocaval ligament (Makuuchi ligament) arises between the liver and the lateral edge of IVC. Right hepatic vein is invested by this ligament. While exposure of RHV, this ligament is to be taken down. 9 The study of retro hepatic IVC relevance for hanging maneuver liver resection is being published in various out safe plane for tunneling and distance of Fossa venacava. It will a guide a surgeon for tunneling during hanging maneuver, useful in anterior approach liver resection.

Methods
This is a cross-sectional observational study carried out at College of Medical Sciences, Bharatpur, Chitwan. A total of 26 livers preserved in formalin were used for the study. These specimens were once used by the Department of Anatomy for gross anatomical teaching for students, since the establishment of the college.
Among 26 liver specimens only 20 livers could be utilized for the study. Six livers had damaged IVC or already detached IVC. The posterior wall of the inferior venacava was incised vertically at the midline, two edges were anterior luminal wall (Figure 1 and 2). Each vein that drains into IVC was studied.
The distance between RHV and MHV known as Fossa venacava was measured. Two landmarks were drawn at opening of IRHV and Caudate vein. The horizontal distance between these two lines is known as Vein gap and the distance was measured using a digital Vernier caliper. Fossa venacava and Vein gap provide a safe plane for forceps insertion while tunneling the interface between the At inferior surface of IVC, a wire was inserted just medial to IRHV, known as right course of forceps insertion. Similarly at the midline (11-12 O'clock) position wire was inserted known as the Intermediate course of forceps insertion and at the medial edge of Caudate vein, a wire was inserted known as left course of forceps insertion (Figure 3).
All the collected data was entered and analyzed SPSS-20. Descriptive variables were described using frequency and percentage. Continuous variables were described using mean and standard deviation
Middle and Left hepatic vein had common trunk in 60% of specimen while 40% had separate insertion in IVC. The hepatic vein had extra hepatic course in 80% of specimen, while in 20% of cases hepatic vein inserted into IVC intraparenchymally.
Inferior right hepatic vein was present in 60% of cases and were multiple IRHV in 10% of cases. Caudate vein was present in 85% of cases and were multiple in 35% of cases.

Discussion
Liver hanging maneuver is already an established standard technique during anterior resection. The safety of this technique depends upon safer tunneling between retro hepatic inferior venacava and liver. 1,10,11 A detail anatomical knowledge provide a guidance for safer tunneling plane. these vessels while tunneling. 8 Our study suggests at least a 5.8 mm gap and shows little risk of injury compared to the did not study vessels less than 3mm as there will be selfhemostasis of such vessels when injured.
out the safest course. We found the intermediate course being the safest. When there is an absent IRHV, it is always wise to undergo the right course of forceps insertion as it is the safest course found in an absent IRHV specimen. A similar result was described by Hirai et al.
The average diameter of MRHV and IRHV in our study was 9±4.32 mm and 6.1 ±0.98 mm respectively. A similar result was found in a study conducted by Sato et al. 6 During they need to be reconstructed to prevent congestion in the recipient's liver.

Conclusion
While tunneling during the hanging maneuver, the Fossa venacava has a very small distance, so we suggest Vein gap is also short; hence Intermediate course of forceps insertion provides the safest route for tunneling during hanging maneuver liver resection. The diameter of IRHV and MRHV is most of the time big, hence, to prevent congestion it is always advised to reconstruct such vessels whenever possible.